1. Field of the Invention
The present invention relates to (1) a polymer, (2) a chemically amplified resist composition containing the said polymer, and (3) a patterning process using the said chemically amplified resist composition. Meanwhile, a high energy beam in the present invention includes a ultraviolet beam, a deep ultraviolet beam, an electron beam, an EUV, an X-ray, an excimer laser beam, a γ-beam, and a synchrotron radiation beam.
2. Description of the Related Art
In recent years, as LSI progresses toward a high integration and a further acceleration in speed, a miniaturization of a pattern rule is being sought; and in this trend, deep ultraviolet beam lithography and vacuum ultraviolet lithography are considered to be viable next generation microprocessing technologies. In particular, a photolithography using an ArF excimer laser beam as a light source is an indispensable technology for ultramicroprocessing with the size of 0.13 μm or less.
The ArF lithography had been partly used since manufacturing of the device with the node of 130 nm; and this became a mainstream lithography technology since the device with the node of 90 nm. As the next lithography technology for the node of 45 nm, the lithography using an F2 laser beam having a wavelength of 157 nm had been considered to be viable at first; but delay of development thereof was expected due to some problems. Then, the ArF immersion lithography, in which a liquid having a higher refractive index than an air, such as water, ethylene glycol, and glycerin, is inserted between a projector lens and a wafer thereby enabling to design the projector lens having the numerical aperture (NA) of 1.0 or more so as to accomplish high resolution, has been receiving an attention rapidly (for example, see Journal of Photopolymer Science and Technology, Vol. 17, No. 4, p 587 (2004)); and this technology is now in the stage of practical use. In this immersion lithography, a resist composition not easily leaching into water is required.
In the ArF lithography, a resist composition having high sensitivity capable of achieving sufficient resolution with small exposure dose thereby deterioration of an expensive optical material of a high precision may be avoided is required; and to this end, selection of a component that is highly transparent at the wavelength of 193 nm is the most generally used measure. For example, polyacrylic acid and its derivative, an alternative copolymer of norbornene and maleic anhydride, polynorbornene and a ring-opened metathesis polymer, and a hydrogenated ring-opened metathesis polymer have been proposed as the base polymer thereof; and this approach has been giving somewhat satisfactory results in terms of enhancing transparency of the resin itself.
To achieve high resolution, various photo acid generators and additives have been investigated. For example, it is generally known that high resolution can be obtained by adding a basic compound such as an amine as a quencher to control diffusion of an acid that is generated by photo-exposure. Alternatively, a function to control acid diffusion can also be acquired by using two or more photo acid generators wherein one of them is an onium salt generating a so-called weak acid (Japanese Patent Laid-Open (Kokai) No. 2010-155824 and Japanese Patent Laid-Open (Kokai) No. 2008-158339). That is, when an onium salt generating a strong acid such as a fluorinated sulfonic acid and an onium salt generating a weak acid such as a carboxylic acid and a sulfonic salt not substituted with a fluorine atom are used as a mixture of them, a strong acid generated from the photo acid generator by exposure to a high energy beam collides with the unreacted onium salt containing an weak acid whereby releasing the weak acid by a salt-exchange reaction and forming an onium salt having a strong acid anion. In this process, the strong acid is changed to the weak acid having a less catalytic performance; and thus, the acidic activity is apparently lost thereby resulting in that the acid diffusion can be controlled. Here, in the case that a photo acid generator generating a strong acid is an onium salt, the strong acid generated by exposure to a high energy beam can be changed to a weak acid, but a weak acid generated by exposure to a high energy beam cannot undergo a salt-exchange reaction by colliding with an unreacted onium salt generating a strong acid. These are caused by the phenomenon that the onium cation forms an ion pair with a stronger acid anion easily. However, an onium salt generating a weak acid is migratable and diffusible in itself in a resist composition thereby affecting lithography performance, causing leaching into an immersing liquid, and so on; and thus, there remains a problem in attaining high resolution.
Further, a resin-bonding type onium salt whose weakly acidic anion is bonded to a resin has been developed (WO2010119910 and Japanese Patent Laid-Open (Kokai) No. 2011-37834). With this, it became possible to control migration and diffusion of the onium salt having a weak acid; but there still remains a problem in overcoming a defect such as peel-off of a resist pattern from a substrate, the phenomenon often found in a resist added with a weakly acidic anion.